1. Field of the Invention
This invention relates to a mower suspension apparatus for suspending a mower unit from a vehicle body of a lawn tractor.
2. Description of the Related Art
Broadly, lawn tractors may be classified into two types. One is the ground-engaging type in which the mower unit is operable to cut grass while contacting the ground through auxiliary wheels. The other is the suspension type in which the mower unit is operable to cut grass while being suspended from the vehicle body to be afloat a predetermined distance above the ground The suspension type includes mid-mount type lawn tractors as disclosed in Japanese Patent Laying-Open Publications H9-328019 and H9-272350. Each of the mower units disclosed in these publications is suspended from the vehicle body through a total of four links, i.e. a pair of right and left front links and a pair of right and left rear links, to be capable of parallel vertical movement. The mower unit is vertically movable by vertically swinging the right and left rear links with a hydraulic cylinder, for example.
The suspension type mower unit basically is supported solely by the vehicle body, so that the entire weight of the mower unit acts on the vehicle body. Thus, this type of mower unit has advantages over the ground-engaging type mower unit in that a grass cutting height may be adjusted easily, and that the mower unit may be constructed lightweight or may be simplified.
On the other hand, however, the suspension type mower unit has the following drawback occurring on a sideways sloping ground, depending on such conditions as an angle of inclination and hardness of the turf. That is, the conventional lawn tractor has a mower unit suspended parallel to the vehicle body. When, for example, the right side of the vehicle body is higher than the left side, a shift in the center of gravity may cause the left wheels to sink deeper into the ground or become dented to a greater extent than the right wheels. This results in the vehicle body inclining to a greater degree than the angle of inclination of the ground. Then, the mower unit inclines by an acute angle to be no longer parallel to the ground. In this example, the mower unit inclines further rightward.
Then, the cutting height increases at the right side, and decreases at the left side. As a result, the mower unit leaves two uneven adjacent rows of grass.
The object of this invention is to provide a mower suspension apparatus with an improved suspension structure to mitigate the above drawback encountered on a sideways sloping ground, while maintaining the advantage of the suspension type.